Add upgrade step for new configuration registry value

When upgrading `plone.app.multilingual` from version 1.1 to 1.2.x the following error occurs:

    KeyError: 'Interface `plone.app.multilingual.interfaces.IMultiLanguageExtraOptionsSchema` defines a field `bypass_languageindependent_field_permission_check`, for which there is no record.'

This happens because ``IMultiLanguageExtraOptionsSchema`` introduces a new field/configuration registry record, but not upgrade step is provided.

This PR adds an upgrade step to create that record, if necessary.